In the construction of V-cell air filters a sheet of relatively heavy gauge, wire mesh or screen is folded in a V-shape or series of adjacent V-shapes to form a supporting frame with a plurality of such "cells" for supporting an overlying fibrous filter media. Most prior art filters of this type also include a rectangular metal frame to support the edges of the wire screen in position across the air flow conduit, and triangular sheet metal caps across the open tops and bottoms of the V-cells to close off and stabilize the upper and lower ends of the wire mesh frame. A filter cell of this type is generally illustrated and described in U.S. Pat. No. 3,984,221 although the claims of such patent are primarily directed to an improved retaining strip for the filter media of such filters.
Two significant problems have existed in the abovementioned and other similar prior designs of V-cell filters. One problem is caused by the retainers and frame areas in prior devices, which are dead areas as far as the passage of air is concerned. In a high velocity system (approximately 1500 fpm) such "dead areas" become a limiting component by considerably increasing the size and capacity of the fan motors required to maintain the even flow of air therethrough. This increased fan size is required because in such prior systems the dead areas led to a pressure drop of 1.5 inches of mercury at air velocities of 1500 fpm. Consequently the increased horsepower requirements for the fan motors increase the energy requirements to operate the system, making the system significantly more expensive to purchase and maintain. This problem is more acute than may first seem, because fan motor size varies according to the cube of the ratio of pressure drops. For example doubling the pressure drop requires a fan motor increase of eight-fold.
A second problem in prior V-cell filters may also be attributed to the substantially dead or blocked areas, and the need to increase the effective areas of exposed filtering media through which air passes to maximize filter efficiency. The effective filter area is measured by the ratio of filter surface area to conduit cross-sectional area. Prior attempts at V-cell filters have been able to achieve such a ratio of only about 7.5 to 1. A prior attempt to locate a common solution to the undesirable high pressure drop and to the need for maximizing filter surface area resulted in the removal of considerable portions of the retainers and sheet metal frame surface in the cells, and replacing these areas with fibrous filter media. This solution utilized a plurality of cut wire mesh sections so connected as to form a substantially open V-cell wire mesh arrangement. The filter media was laid into the V-cell and clamps in the form of two plates bolted to the screen applied at the forward or upstream edges to hold the media in place.
The aforementioned approach was somewhat effective to significantly reduce the pressure drop and maximize effective filter area. However, while the improved V-cell design improved these two important problems, new problems in attaching the new filter media to the frame and in stabilizing the cell to decrease vibration and noise were created. The bag-like filter media was difficult for maintenance personnel to attach and therefore the bags were often incorrectly replaced resulting in poor filtration. Additionally, the excess time spent changing the bags significantly increased system down time.
It is to an improved means for connecting the separate wire mesh V-cells and for attaching filter media thereto that the present invention is directed.